DE2841428C2 - - Google Patents

Description

The invention relates to a receiver for the compatible Receiving stereophonic signals according to the preamble of the claim 1.

Such a receiver device is proposed in the older, not prepublished DE-OS 27 15 741. This receiver device works with synchronous demodulators for demodulating the received signals in order to be able to generate the sum signal (L + R) and the difference signal (LR) and ultimately the stereophonic signals (L, R) . In this known receiver device, the tuning process can be regarded as not entirely satisfactory, since beats from the low-frequency channels would have to be kept away during the tuning process.

The invention is therefore based on the object of a generic To design receivers with a simple structure so that improved coordination will be achieved.

This object is achieved with a generic Recipient by the characteristics of the characteristic Part of claim 1 solved.

A key concept of the invention can therefore be seen in designing the amplitude demodulator as an envelope demodulator, which forwards the sum signal L + R generated at its output to a matrix, in addition to which the PM demodulator, which outputs an output signal proportional to (LR ) × cos Φ is generated, is connected to the matrix via a correction circuit, at the output of which the stereophonic signals L and R are obtained.

A receiver device with the generic is comparable, is from Electronics, April 14, 1977, p. 82 (Magnavox way) known. The recipient's vote there, however, causes even greater difficulties than with the aforementioned generic receiver.

In an expedient development of the invention, the correction circuit is designed with a limiter circuit for the IF signal, a phase-locked circuit and with a cosine phase detector, the output signal of which is proportional to cos Φ . In this way it is possible, in an advantageous embodiment, to obtain an output signal at the output of a divider circuit which is proportional to the difference signal (LR) .

To further improve the tuning process, the matrix is preceded by a switch which only switches the difference signal (LR) through to the matrix when the phase-locked circuit is engaged. In this respect, the corresponding monophonic or stereophonic signal can only be obtained at the output of the matrix when the tuning has ended.

The invention is described below using a schematic Embodiment by means of a block diagram of a receiver explained in more detail in the single figure.

The receiver shown in the drawing is intended to receive a compatible AM stereo signal from a transmitter, as described in the older DE-OS 27 15 741. According to this DE-OS, a transmission signal from a transmitter for a monophonic receiver is compatible in such a way that the carrier of the transmission signal is amplitude-modulated with a monophonic signal, in accordance with the expression (L + I + R) , so that the entire stereo information phase modulation is included. The carrier is modulated with the sum (L + R) and the difference LR) in a 90 ° phase shift, so that the change in amplitude is eliminated and only the phase change remains. Then an amplitude modulation with (1+ L + R) takes place in a corresponding modulator. The transmission signal then becomes

(1 + L + R) cos [ (w _c t + arc tg (L - R) / (1 + l + R) ].

In the exemplary embodiment of a receiver according to the invention, a compatible AM stereo signal of the form specified above is received via the antenna 10 . This signal is processed in the usual way in an RF stage 11 and in the IF stage 12 . The monophonic signal, which is represented by the sum signal L + R , is obtained in that the output of the IF stage 12 is connected to an envelope demodulator 13 . The signal L + R is then fed to a matrix 14 . A detector 26 with automatic gain control can be arranged in a feedback loop between the output of the envelope demodulator 13 and the IF stage 12 in order to control the gain of the IF stage 12 in a manner known per se.

The output of the IF stage 12 is also connected to a synchronous detector or PM demodulator 16 and to a limiter stage 17 . The limiter stage 17 is connected to an input of a phase detector which, together with a low-pass filter 19 and a voltage-controlled oscillator 20, forms a phase-locked circuit 22 . From this circuit 22 , an output signal (sin w _c t) is fed to the PM demodulator 16 .

An output signal of the limiter stage 17 , which contains only the transmitted phase information, is fed to a cosine phase detector 23 as an output signal (cos w _c t) and to the phase-locked circuit 22 , which is designed as a feedback loop. The cosine phase detector 23 is a multiplier stage which corresponds, for example, to the Motorola MC 1595 type, which is a four-quadrant multiplier.

The instantaneous phase difference between the two carrier frequencies, which means the unmodulated and the transmitted carrier frequency, is sampled in the cosine phase detector 23 and represents the correction information which is necessary in order to restore the original stereo signals L, R.

The desired correction information is a signal which corresponds to the cosine of Φ or the

cos arc tg [ (L - R) / (1 + L + R) ]

or

is proportional. The correction information is fed to a divider circuit 25 , which also receives an output signal of the PM demodulator 16 . At the output of the divider circuit, LR is obtained, which is the desired stereo difference signal.

However, until the receiver is properly tuned, the output of phase locked circuit 22 is not a function of w _c t, but a function of a frequency approaching w _c t . The difference frequency would accordingly occur in the correction signal at the output of the cosine phase detector 23 and cause an undesired output signal in the difference channel.

The output of the cosine phase detector 23 is therefore with a low-pass filter 27 with z. B. 2 to 10 Hz, in which the average DC voltage level of the output signal is used to control a switch 28 for switching between mono and stereo. The switch 28 is voltage controlled and set so that it remains in the monophonic position until the phase-locked circuit 22 locks onto the frequency w c t . Only then does it switch to a stereophonic position.

In monophonic operation, only the L + R signal is fed to the matrix 14 , only this monophonic low-frequency output signal being used for tuning the receivers. If the receiver is tuned and if the circuit 22 is locked to w _c t , the DC voltage level of the cosine phase detector 23 at the output after filtering by the low-pass filter 27 is sufficiently high to switch the mono / stereo switch 28 to the stereophonic Switch operating mode. This enables the LR signal to be fed to the matrix 14 which provides L and R separately at their output terminals.

Regarding the received signal, it should be noted that the output signal of the IF stage 12 is the expression

(1 + L - R) cos (w _c t + Φ )

is proportional, the following relationship applies:

Φ = arc tg [ (L - R) / (1 + L + R) ].

The output signal of the envelope demodulator 13 becomes proportional to L + R. The output signal of the limiter stage 17 becomes proportional to cos (w _c t + Φ ) and the output signals of the phase-locked circuit 22 become proportional to sin w _c t and after a phase shift also proportional to cos w _c t . The output signal of the synchronous detector or the PM demodulator 16 is the product of

(1 + L + R) cos (w _c t + Φ ) and sin w _c t .

Neglecting the term with the double frequency 2 w _c t and taking into account the fact that

Φ = arc tg (L - R) / (1 + L + R)

it can be seen that the product is proportional to LR) cos Φ . The output signal of the cosine phase detector 23 becomes proportional to cos Φ and the output signal of the divider circuit 25 thus becomes proportional to (LR) cos Φ / cos Φ or (LR) . With the input signals (L + R) and (LR) , the matrix delivers 14 output signals L and R.

Claims (4)

1. Receiver for compatible reception of stereophonic signals (L, R) , the carrier wave of which is amplitude-modulated in proportion to the sum (L + R) of the stereophonic sound signals and proportional to an angle is phase modulated, wherein C ₁ and C ₂ are constants.
with an IF stage ( 12 ) which emits the received signal as an intermediate frequency signal,
with a correction circuit ( 25, 17, 23, 22 ) which effects a division by a correction signal derived from the IF signal proportional to cos R ,
with an AM demodulator,
with a PM demodulator ( 16 ) designed as a synchronous detector and
with a matrix ( 14 ) for generating the stereophonic sound signals (L, R) from the sum signal (L + R) and the difference signal (LR) ,
characterized,
that the AM demodulator is designed as an envelope demodulator ( 13 ), which is connected to the IF stage ( 12 ) and outputs the sum signal (L + R) to the matrix ( 14 ), that the PM demodulator also with the IF stage ( 12 ) is connected and generates an output signal proportional to (LR) cos Φ and
that the PM demodulator ( 16 ) is connected to the matrix ( 14 ) via the correction circuit ( 25, 17, 23, 22 ). 2. Receiver according to claim 1, characterized in that the correction circuit ( 25, 17, 23, 22 ) has a limiter circuit ( 17 ) for the IF signal, a phase-locked circuit ( 22 ) connected downstream thereof and one with the limiter circuit and the phase-locked circuit Connected cosine phase detector ( 23 ), the output signal is proportional cos Φ . 3. Receiver according to claim 2, characterized in that the correction circuit ( 25, 17, 23, 22 ) contains a divider circuit ( 25 ) which from the output signals of the PM demodulator ( 16 ) and the cosine phase detector ( 23 ) generates an output signal proportional to the difference signal (LR) . 4. Receiver according to claim 3, characterized in that between the divider circuit ( 25 ) and the matrix ( 14 ) a switch ( 28 ) is arranged, which receives a control signal from the phase-locked circuit ( 22 ) via a low-pass filter ( 27 ) , such that the signal path for the differential signal (LR) is switched through only when the phase-locked circuit ( 22 ) is engaged.